1. Field of Invention
This invention relates generally to a wire coated with a coating applied electrostatically and a process for producing such coated wire. The coated wire finds particular application in a hybrid scavengeless development (HSD) apparatus for ionographic or electrophotographic imaging and printing apparatuses and machines. Use of the coated wire in an HSD developer unit assists in preventing toner or other particulate contamination of the wires in such an HSD developer unit.
2. Description of Related Art
Generally, the process of electrophotographic printing includes charging a photoconductive member to a substantially uniform potential to sensitize the surface thereof. The charged portion of the photoconductive surface is exposed to a light image from either a scanning laser beam, an LED source, or an original document being reproduced. This records an electrostatic latent image on the photoconductive surface, the latent image conforming to the original image. After the electrostatic latent image is recorded on the photoconductive surface, the latent image is developed by contacting it with an electrostatically attractable powder known as "toner." Thus, a toner image is produced in conformity with a light image of the original being reproduced. The toner powder image is subsequently transferred to a substrate, e.g., paper. Finally, the toner powder image is heated to permanently fuse it to the substrate in image configuration.
In the process of electrophotographic printing, the step of conveying toner to the latent image on the photoreceptor is known as development. The object of effective development of a latent image on the photoreceptor is to convey toner particles to the latent image at a controlled rate so that the toner particles effectively adhere electrostatically to the charged areas on the latent image. A commonly used technique for development is the use of a two-component developer material, which comprises, in addition to the toner particles which are intended to adhere to the photoreceptor, a quantity of magnetic carrier beads. The toner particles adhere triboelectrically to the relatively large carrier beads, which are typically made of steel. When the developer material is placed in a magnetic field, the carrier beads with the toner particles thereon form what is known as a magnetic brush, wherein the carrier beads form relatively long chains that resemble the fibers of a brush. This magnetic brush is typically created by means of a "transport" roll. The transport roll is typically in the form of a cylindrical sleeve rotating around a fixed assembly of permanent magnets. The carrier beads form chains extending from the surface of the transport roll, and the toner particles are electrostatically attracted to the chains of carrier beads. When the magnetic brush is introduced into a development zone adjacent the electrostatic latent image on a photoreceptor, the electrostatic charge on the photoreceptor will cause the toner particles to be pulled off the carrier beads and onto the photoreceptor.
Another known development technique involves a single-component developer, that is, a developer that consists entirely of toner. In a common type of single-component system, each toner particle has both an electrostatic charge (to enable the particles to adhere to the photoreceptor) and magnetic properties (to allow the particles to be magnetically conveyed to the photoreceptor). Instead of using magnetic carrier beads to form a magnetic brush, the magnetized toner particles are caused to adhere directly to a transport roll. In the development zone adjacent the electrostatic latent image on a photoreceptor, the electrostatic charge on the photoreceptor will cause the toner particles to be pulled from the developer to the photoreceptor. (As used in the claims herein, the phrase "developer material" shall be construed to mean either single-component or two-component developer material, or a portion thereof, such as the toner separated from the two-component developer material on a magnetic brush.)
The electrophotographic marking processes given above can be modified to produce color images. One color electrophotographic marking process, called image-on-image (IOI) processing, superimposes toner powder images of different color toners onto the photoreceptor prior to the transfer of the composite toner powder image onto the substrate. While the IOI process provides certain benefits, such as a compact architecture, there are several challenges to its successful implementation. For instance, the viability of printing system concepts such as IOI processing requires development systems that do not interact with a previously toned image. Since several known development systems, such as conventional magnetic brush development and jumping single-component development, interact with the image on the receiver, a previously toned image will be scavenged by subsequent development if interacting development systems are used. Thus, for the IOI process, there is a need for scavengeless, or noninteractive, development systems.
In a scavengeless development system, toner is made available to the photoreceptor by means of AC electric fields supplied by electrode structures, commonly in the form of wires extending across the photoreceptor, positioned within the nip between a donor roll and photoreceptor. The spacing between the wires and the donor roll is on the order of the thickness of the toner or less, and under certain operating conditions, the wires may be in contact with the donor roll.
A typical hybrid scavengeless development apparatus includes, within a developer housing, a transport roll, a donor roll, and an electrode structure. The transport roll operates in a manner similar to a development roll in a conventional development system, but instead of conveying toner directly to the photoreceptor, conveys toner to a donor roll disposed between the transport roll and the photoreceptor. The transport roll is electrically biased relative to the donor roll, so that the toner particles are attracted from the transport roll to the donor roll. The donor roll further conveys toner particles from the transport roll toward the photoreceptor. This donor roll generally consists of a conductive core covered with a thin (50-200 .mu.m) partially conductive layer. In the nip between the donor roll and the photoreceptor are the wires forming the electrode structure. During development of the latent image on the photoreceptor, the electrode wires are AC-biased relative to the donor roll to detach toner therefrom so as to form a toner powder cloud in the gap between the donor roll and the photoreceptor. Typical ac voltages of the wires relative to the donor roll are 700-900 Vpp at frequencies of 5-15 kHz. These AC signals are often square waves, rather than pure sinusoidal waves. The latent image on the photoreceptor attracts toner particles from the powder cloud, forming a toner powder image thereon.
A problem with developer systems using wires is that toner and/or toner constituents buildup on the wires over time and result in development defects. Wire contamination is a first class of defect in which toner and/or toner constituents buildup on the wire side that is in contact with the donor roll. Wire history is a second class of defect in which toner and/or toner constituents buildup on the wire side away from the donor roll. Constant cleaning of the wires is required in order to alleviate the above-defects, which cleaning is time-consuming and inefficient in that it requires machine downtime.
U.S. Pat. No. 6,049,686 sought to address the above-identified problems, the patent describing a hybrid scavengeless development apparatus and a method for preventing wire contamination. As in the standard hybrid scavengeless development method discussed above, a voltage supply is provided for electrically biasing the electrode wires during a developing operation with an alternating current (AC) bias to detach marking particles from the donor member, forming a cloud of marking particles in the development zone, and developing the latent image with marking particles from the cloud. In the process of this patent, however, the voltage supply periodically electrically biases the electrode wires during a cleaning operation with a direct current (DC) bias and with an alternating current bias so that toner is effectively removed from the wire. The bias levels are chosen to reduce field-induced redeposition of right or wrong sign toner.
What is desired is a more efficient and effective method of preventing toner constituent build-up on the wires in the first instance, thereby substantially reducing or eliminating the frequency of needed cleaning operations of the wires, and also substantially reducing or eliminating image quality defects that might otherwise be caused by such buildup.